1. Field of the Invention
This invention relates to a tray assembly for a steam boiler feedwater deaerator. Each trough of the assembly has a V-shaped configuration and inclined, outwardly-extending, notched walls for positively guiding the water to be deaerated toward an area vertically above an underlying trough and promoting more uniform water dispersion in the tray section.
2. Description of the Prior Art
Deaerators have long been used for the removal of corrosion causing gases such as oxygen and carbon dioxide that are dissolved within the feedwater of steam systems. A power plant, for example, could deteriorate rapidly from the ravages of corrosion if substantially complete removal of the dissolved oxygen is not effected. Moreover, use of high pressure cycles in today's steam systems has resulted in an even greater need to protect expensive components in the feed cycle from corrosion.
Certain of the feedwater deaerators in use today utilize a two-stage method for attaining reliable, specififed performance over a varying load range. In the first stage, incoming feedwater is directed through a nozzle to form a thin walled, hollow cone spray pattern within a steam filled vent condensing chamber. In this stage latent heat transfer is instantaneous due to the intimate water-to-steam exposure. As the sprayed feedwater reaches the lower portions of the vent condensing chamber, the water temperature is within about 2.degree. F. of the saturated steam temperature of the counterflowing steam, and a portion of the dissolved oxygen and free carbon dioxide have been removed, due to the effects of Henry's law of partial pressures.
In the second stage of such deaerators, the sprayed feedwater enters a tray assembly or stack. In the past, such tray stacks have comprised tiers of elongated, rectangular troughs which are horizontally spaced in side-by-side relation in each tier, and the tiers are vertically spaced and arranged so that the troughs are in staggered relationship to troughs in adjacent tiers. As such, the feedwater flows into the uppermost troughs and then overflows into underlying troughs, in a generally downward, zig-zag path through a countercurrent, uprising flow of pure steam. In this stage, the water immediately reaches saturation temperature such that the counterflowing steam can effectively scrub and remove the final traces of oxygen and carbon dioxide. The water leaving the lowermost portions of the tray stack is "stripped" by the purest stream that enters the deaerator, whereupon the water then flows into a storage receptacle for later reintroduction into the steam boiler cycle.
It has been found that while the rectangular deaerator trays referenced hereinabove are entirely satisfactory for use in many types of installations, occasionally situations are encountered wherein it is necessary to reduce dissolved oxygen levels in the feedwater exiting the deaerator to values difficult to attain with rectangular trays. The configuration of some types of rectangular troughs is such to cause water overflowing the top edges of the troughs to travel exteriorly down the vertical sidewalls of the troughs and then move in clinging fashion toward the center of the horizontal trough bottom, due to the surface tension of the feedwater as well as the adhesion of the feedwater droplets to the bottom of the trough. The droplets often remain momentarily near the center of the trough bottom underside, and then fall vertically toward the space between the underlying troughs thereby effectively bypassing an entire tier of troughs and instead falling into the troughs of the second underlying tier. As a consequence, it is somewhat difficult to attain extremely low dissolved oxygen levels in the feedwater exiting the second stage.
In the past, certain deaerators have been provided with rectangular troughs having sidewalls which extend beneath the trough bottom, in an attempt to insure that the individual feedwater droplets do not cling to the underside of the trough bottom. In some cases, the vertical sidewalls have been provided with a serrated edge to assist in dispersing the feedwater. However, there is still a need in the art for use in certain installations of a deaerator to provide more complete removal of the dissolved oxygen in the feedwater to insure that the steam system is exposed to the least amount of corrosive gases.